1. Field of the Invention
This invention concerns fuel delivery systems and more particularly concerns fuel delivery systems for compression ignition fuel injected internal combustion engines.
2. Description of the Prior Art
The need for sharply reduced noxious emissions from conventional spark ignition carbureted internal combustion engines has led to a decrease in the compression ratios of these engines which in turn has led to a sharply decreased thermal efficiency due to a loss in volumetric efficiency. This is at a time when the efficiency of the engine is becoming increasingly important with the greatly increased costs of petroleum fuels. Diesel engines have not been required to be changed in design to reduce their compression ratios and hence still exhibit relatively good thermal efficiency. However, diesel engines heretofore have been quite expensive to manufacture due to various factors, not the least of which is the high precision variable volume fuel injectors. These injectors must operate at sufficiently high pressure to provide good atomization of the fuel as it is injected into the combustion chamber and in addition the quantity of fuels injected by the injector mechanism must be capable of being varied precisely in order to vary the power output of the engine. The operating requirements of the fuel injectors have contributed substantially to the overall expense of manufacturing these engines and has limited the application of such engines to passenger cars.
While injection mechanisms such as disclosed in the patent to Braren, U.S. Pat. No. 1,736,647, have heretofore been proposed in which the atomization of fuel in the combustion chamber has been aided by the intermixture of a quantity of air in the fuel prior to injection, the fuel injector mechanisms disclosed in that patent are still of variable volume design since the variation in fuel-air mixture available for control of the power output is extremely limited. This is so since the Braren patent discloses a mixture of a relatively minute quantity of air in the fuel such as to entrain air bubbles within the fuel mixture which will expand upon injection to aid in the atomization process. The proportions recited in that patent, i.e., a minimum proportion of fuel is such that the mixture is essentially liquid and remains a liquid or emulsion, as the patent describes it, during injection into the cylinders. Thus, a variable volume injector which is operated at fairly high pressures would still be required in a fuel delivery system according to that patent to provide a practical range of power output of the engine.
A second aspect of the approach of Braren is that all the atomization is still carried out upon injection into the combustion chamber, such that relatively high pressures of the injector are required, which requirement is made more difficult to meet by the compressibility of the liquid-air mixture. Also, the complete vaporization of the fuel in the air compressed in the combustion chamber is not insured.
The time lag between atomization of the fuel in the combustion chamber and the change of state into the vapor phase in conventional diesel engines affects the operating efficiency thereof, causing them to operate at relatively slow speed.
It is therefore an object of the present invention to provide a fuel delivery system for compression ignition fuel injected internal combustion engines in which a constant volume fuel vapor gas injector may be provided which may operate at relatively low pressures.
It is a further object of the present invention to provide a fuel delivery system in which complete and total vaporization of a fuel occurs and is maintained prior to injection such that complete combustion of the fuel in the combustion chamber is insured.
It is a further object of the present invention to provide such a fuel delivery system which is relatively simple in design and rugged in construction such as to insure good reliability in the automotive environment.